The heart is sometimes incapable of providing sufficient pumping capacity to meet the needs of the body. The effects of this inadequacy can be alleviated by providing a mechanical pump referred to as a mechanical circulatory support device (“MCSD”). An MCSD can be implanted to supplement the pumping action of the heart, most commonly for an extended period of time such as several years.
An MCSD is most commonly connected to the left ventricle. In this arrangement, an inlet end of the pump, or an inlet cannula connected to the inlet end of the pump, is implanted in the wall of the ventricle, such as at the apex of the ventricle. An outlet cannula is connected between the outlet end of the pump and an artery such as the aorta. MCSDs which are connected to a ventricle commonly are referred to as ventricular assist devices or “VADs.” During operation, the VAD assists the heart to pump blood from the left ventricle to the aorta.
Certain MCSDs are typically connected to the heart through the use of a mounting ring, as disclosed in U.S. Published Patent Application Nos. 2004/0171905, 2007/0134993, and 2015/0112120 (“the '120 Publication”), the disclosures of which are hereby incorporated by reference herein. A mounting ring has a body and a main bore extending through the body, and also has features which can be used to attach the body to the outside of the heart wall so that the bore extends towards and away from the wall. For example, some mounting rings are equipped with a ring of fabric encircling the body, so that the mounting ring can be secured in place by suturing. Other mounting rings are equipped with barbs or other fasteners for attaching the body of the ring to the heart wall. The mounting ring is arranged so that a portion of the body defining at least part of the main bore is compressible to constrict the bore around an element of the MCSD to hold the element in place. As shown, for example, in the aforementioned U.S. Published Patent Application No. 2007/0134993 (“the '933 Publication”), the body may include a base plate which faces toward the body when the ring is installed, and a pair of generally C-shaped arms encircling the main bore. The arms have fixed ends attached to the base plate near one location on the circumference of the bore. At least one of the arms is attached to the base plate only at and near its fixed end, so that the portion of the arm remote from the fixed end is free to bend towards the opposing arm. A clamp is provided for squeezing the arms together to constrict the main bore.
The mounting ring may also incorporate an element referred to as a gimbal ring. The gimbal ring is a generally hoop-shaped element which defines a gimbal ring bore. The gimbal ring is disposed inside the main bore defined by the body. The gimbal ring may have a spherical outer surface, and the main bore may have a corresponding interior surface, so that the gimbal ring can pivot to tilt the axis of the gimbal ring bore relative to the main bore and thus relative to the body of the mounting ring. The gimbal ring typically is formed from a relatively hard polymeric material, and is provided with a slot extending through the wall of the ring at one point around its circumference. Thus, when the main bore is constricted, the mounting ring can be compressed slightly to constrict the gimbal ring bore.
A one-way valve may be mounted within the gimbal ring bore. The one-way valve typically is formed as a tubular or ring-like structure with flaps or collapsible sections which can close to occlude the gimbal ring bore.
In use of such a mounting ring, the base of the body is secured to the outside of the heart. A cruciate cut is made in the heart wall within the gimbal ring bore and a separate surgical tool is used to core a hole in the heart. The valve temporarily occludes the gimbal ring bore to prevent massive blood loss when the coring tool is removed. A pump, an inlet cannula or other element of an MCSD is, is then inserted through the interior of the valve and through the gimbal ring bore into hole into the heart. The gimbal ring can be tilted to align the axis of the MCSD element with the anatomical features of the heart. Once the MCSD element has been positioned as desired, clamp is tightened to constrict the main bore and thus constrict the gimbal ring bore to secure the MCSD element in position. The MCSD element must be secured so as to remain in place during operation, despite the loads imposed by the beating heart and by movement of the patient. While mounting rings of this type have been very effective, it is sometimes difficult to tighten the clamp sufficiently.